1. Field of the Invention
The present disclosure provides methods for depositing oxide thin films by atomic layer deposition (ALD). More particularly thin films comprising silicon dioxide are deposited using disilane compounds.
2. Description of the Related Art
Silicon dioxide is a widely used material in semiconductor industry. It is used for instance as gate oxide and a dielectric layer in dynamic random access memories (DRAM). Recently, other possible applications have evolved that would require good step coverage and good SiO2 filling capabilities, for example shallow trench isolation (STI). Atomic layer deposition (ALD) has been proposed as a possible technique to meet these more stringent requirements. Unfortunately, the growth rate per cycle has traditionally been low for ALD SiO2 processes making the processing economically non-viable. New precursors with higher reactivity enabling higher growth rate are therefore needed.
In its various forms Chemical Vapor Deposition (CVD) is the most frequently used method of producing silicon dioxide (see patent publications JP 9306906, U.S. Pat. No. 4,845,054, U.S. Pat. No. 4,981,724, U.S. Pat. No. 5,462,899, JP 20868486, JP 6158329, JP 80061810, U.S. Pat. No. 4,872,947, JP 7026383, U.S. Pat. No. 5,855,957 and U.S. Pat. No. 5,849,644). Mainly tetraethoxy silane (TEOS) has been used as the silicon source material, and oxygen, water, hydrogen peroxide or ozone have been used as the oxygen source material in the patent publications. In the conventional CVD the oxygen source material is always brought simultaneously with the silicon source material to the growth substrate.
Conventional CVD methods provide neither sufficiently good coverage nor the level of conformality desired for some applications.
Atomic layer deposition (ALD), originally known as atomic layer epitaxy (ALE), is an advanced form of vapor deposition. ALD processes are based on sequential, self-saturated surface reactions. Examples of these processes are described in detail in U.S. Pat. Nos. 4,058,430 and 5,711,811. Due to the self-saturating nature of the process, ALD enables almost perfectly conformal deposition of films on an atomic level and precise control of the thickness and composition of the deposited films.
Silicon dioxide has been grown by ALD processes using compounds such as Si(NCO)4 and N(C2H5)3 (K. Yamaguchi et al., Appl. Surf. Sci. (1998) 130-132) as source materials. Deposition of silicon dioxide by Molecular Layer ALE and UHV-ALE processes using SiCl4 and H2O as source materials is also described in the literature (Surface Review and Letters, Vol. 6, Nos 3 & 4 (1999) 435-448). However, these processes have long reaction times and cannot be realized on an industrial scale.